1. Field of the Invention
The present invention relates to a microphone, and in particular to vibration isolation inside a housing that serves as a microphone grip and supports a microphone unit of the microphone.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-277652 discloses that an air chamber is one element that determines frequency characteristics of a microphone. The air chamber is provided at a rear part of a microphone unit to improve the frequency characteristics over a wide range. For the purpose of achieving excellent frequency characteristics even in low frequency bands, the reactance in the air chamber must be reduced by increasing the volume of the air chamber. In general, a handheld microphone such as a vocal microphone has an air chamber inside a cylindrical housing that serves as a microphone grip. A typical example is described below with reference to FIGS. 2 and 3.
A handheld dynamic microphone 15 includes a cylindrical housing 2 formed by die casting. The microphone unit 3 is supported at one end of the housing 2. Although not shown in the drawings, the microphone unit 3 includes therein a diaphragm to which a voice coil is fixed and a magnetic circuit having a magnetic gap. The voice coil fixed to the diaphragm is vibratably disposed in the magnetic gap. The rear end of the microphone unit 3 is airtightly fit to a connection portion 12 to be attached to one end of the housing 2 with the connection portion 12.
A connector attachment portion 2b is integrally formed at the other end of the housing 2. A connector 4 is mounted in the connector attachment portion 2b. The microphone unit 3 is connected with the connector 4 thorough a lead wire 8. A cavity inside the housing 2 serves as an air chamber 10 at the rear side of the microphone unit 3.
It is preferable to increase the volume of the air chamber 10 for improving sound quality even in low frequency bands. In order to achieve excellent frequency characteristics, intrusion of external air into the air chamber 10 must be prevented. In the dynamic microphone 15, after the microphone unit 3 is connected with the connector 4 through the lead wire 8, a gap between the housing 2 and the connector 4 is sealed with a sealing material 6 such as silicon sealant. Accordingly, the air chamber 10 has an airtight structure.
The housing 2 is generally composed of metal, resin or any other material. Since a gap is formed between the housing 2 and the other components included in the dynamic microphone 15, the housing 2 resonates in response to vibration or impact thereto and generates dissonant noise. In particular, a handheld microphone a user uses by holding the housing (grip) 2 with his/her hand(s) has a significant disadvantage of generation of such vibration. Conventional countermeasures described below have been taken against such a disadvantage on vibration. For resolving the vibration problem, a dumping material such as a rubber 5 is attached to the inner peripheral surface of the housing 2 as shown in FIG. 2 or a sponge 14 is crammed into the housing 2 as shown in FIG. 3. However, these countermeasures are not effective enough to absorb vibration and to prevent noise of the dynamic microphone 15. Another disadvantage is low frequency characteristics of the dynamic microphone 15 if the air chamber 10 of the housing 2 is filled with the sponge 14 as shown in FIG. 3.